1. Field of the Invention
The present invention relates to a withdrawable device of a main circuit for a vacuum circuit breaker, and particularly, to a withdrawable device of main circuit for a circuit breaker capable of being transferred so that a main circuit can is be coupled to or separated from a main frame installed at a rear side of a cradle of a vacuum circuit breaker, and capable of being fixed at a safety position, a test position, and a run position of the vacuum circuit breaker.
2. Background of the Invention
A vacuum circuit breaker serves to protect a power system. The vacuum circuit breaker performs power transmission, power reception, switching, stopping, etc. by using a vacuum interrupter as an extinguisher, and rapidly performs an automatic breaking function when the power system is mal-operated.
And, the vacuum circuit breaker protects a circuit and devices by rapidly interrupting the circuit by an extinguishing function for rapidly spreading an arc into a vacuum vessel, the arc generated when a normal load is open and closed and when an abnormal current is interrupted.
The vacuum circuit breaker largely comprises a main circuit, a transfer carriage, a cradle, and a supplementary device.
The transfer carriage is integrally coupled to the main circuit, and includes a mechanic device for selectively transferring the main circuit to the cradle.
A process for coupling or separating the main circuit to/from the cradle is performed through a tulip contact of the main circuit and a cradle terminal of the cradle. When the vacuum circuit breaker is operated in a state that the main circuit has been coupled to the cradle, a current is introduced into a vacuum interrupter installed in the main circuit through an upper terminal. Then, the introduced current is discharged out through a lower terminal. During this operation, when an accident occurs, the vacuum interrupter instantaneously interrupts the current.
The conventional vacuum circuit breaker and the withdrawable device of a is main circuit for the vacuum circuit breaker will be explained with reference to FIGS. 1 to 3.
FIG. 1 is a perspective view schematically showing a vacuum circuit breaker in accordance with the conventional art, FIG. 2 is a perspective view of a withdrawable device of a main circuit for a vacuum circuit breaker, and FIG. 3 is a planar view of a carriage transfer unit of the withdrawable device of a main circuit for a vacuum circuit breaker.
Referring to FIGS. 1 and 2, the conventional withdrawable device of a main circuit for a vacuum circuit breaker comprises a carriage 100, a cradle 120, a mounting frame 130, a main circuit 140 loaded on the carriage 100, a carriage transfer unit 200 for transferring the carriage 100, a braking unit 204 for limiting a transfer distance of the carriage 100, and a girder assembly 300 for supporting the carriage transfer unit 200.
The carriage 100 includes a box body 101 having a wall body 101a, and two pairs of wheels 102 configured to be inserted into or withdrawn from the cradle 120 along a guide rail installed at an inner side of the cradle 120.
Referring to FIGS. 2 and 3, the carriage transfer unit 200 includes a lead screw 201 inserted into a through hole 101b formed at the wall body 101a of the box body 101 in back and forth directions, a transfer nut 202 screw-coupled to the lead screw 201 and installed at an inner side of the wall body 101a of the box body 101, and a ‘U’-shaped bracket 203 fixed to the box body 101 so as to prevent separation of the transfer nut 202 from the lead screw 201.
The transfer nut 202 is provided with a female screw portion 202a screw-coupled to an outer circumferential surface of the lead screw 201. Two guiding recesses 202b having different depths are formed on upper and lower surfaces of is the transfer nut 202, respectively. And, a guide recess 202c is formed at a central part of the transfer nut 202.
A girder 209 is fixedly coupled to the end of the lead screw 201, and is moved in a rotation direction of the lead screw 201 in a state of being disposed on a pair of travel rails 212 and 212′ installed on a bottom surface of the box body 101 of the carriage 100 in a length direction, i.e., a moving direction of the transfer carriage. The lead screw 201 is coupled to a withdrawable handle 213, and is rotated in a rotation direction of the withdrawable handle 213 by an operator.
The girder assembly 300 includes a support structure 303 having a space 301 therein and supporting bearings so as to transmit a rotation force to the front end of the lead screw 201, right and left sliding plates 304 at both inner sides of the support structure 303 so as to be movable in right and left directions, right and left handles 305′ and 305 fixed to the right and left sliding plates 304 and outwardly protruding from the support structure 303, and a spring 309 for inserting an end 304a into the cradle 120 by outwardly moving the right and left sliding plates 304′ and 304.
The braking unit 204 is provided with forward and backward rotation prevention pins 205 and 205′ in a diagonal direction of the bracket 203 so as to be detachably inserted into the guiding recesses 202b formed on the upper and lower surfaces of the transfer nut 202. And, the forward and backward rotation prevention pins 205 and 205′ are connected to right and left driving pins 207′ and 207 by connection plates 206 and 206′.
The right and left driving pins 207′ and 207 are elastically supported by springs 208′ and 208, respectively. And, the right and left driving pins 207′ and 207 are configured to be pressed by side surfaces of the girder assembly 300 and the girder 209 installed at the ends of the lead screw 201 when the carriage 100 is moved in back and forth directions.
The guide pins 210 are installed at a pair of supporting plates 211 and 211′.
When the backward rotation prevention pin 205′ or the forward rotation prevention pin 205 is separated from the guiding recesses 202b of the transfer nut 202 by the right and left driving pins 207′ and 207, the guide pins 210 are inserted into the guide recess 202c of the transfer nut 202 thus to locate the transfer nut 202 at a front side.
Unexplained reference numeral 141 denotes busbars, 214 denotes bearings, and 500 denotes a withdrawable device.
The conventional withdrawable device of the main circuit for the vacuum circuit breaker may have lowered reliability due to a large number of components and a complicated structure.
More concretely, the withdrawable device includes the transfer nut 202 provided at the carriage transfer unit 200 and performing an idle operation at a run position and a test position of the vacuum circuit breaker, the forward and backward rotation preventing pins 205 and 205′, the connection plates 206 and 206′, the guide pins 210, etc. These components are assembled to each other with a complicated structure. Accordingly, in case that the main circuit 140 and the cradle 120 are assembled to each other in a non-aligned manner, the components may be transformed due to great force in an axial direction. This may cause the vacuum circuit breaker to unstably operate, thereby lowering reliability of the vacuum circuit breaker.
For instance, when the vacuum circuit breaker is moved to a run position from a test position, the guide pins 210 point-contact the transfer nut 202 due to is an axial load occurring when a tulip contact of the main circuit contacts a cradle terminal, and due to an axial load occurring when the main circuit and the cradle terminal are not aligned to each other. As a result, a maximum concentrated load of 500 kgf may occur to damage the guide pins 210. Furthermore, when the vacuum circuit breaker is in the run position or test position, an idle operation is not smoothly performed, but the guide pins may be abraded due to friction.